1. Field of the Invention
The present invention relates to a display apparatus provided with an optical input function, that is, a display apparatus capable of receiving input of information through its display screen by use of light.
2. Description of the Related Art
Generally, liquid crystal display apparatuses are widely used as a display apparatus for cellular phones, laptop computers and the like.
In recent years, techniques have been proposed for providing optical sensors discretely on a display screen of a liquid crystal display apparatus. A liquid crystal display apparatus of this type is capable of receiving input of an image through its display screen by use of an optical sensor. Examples of the technique for receiving input of an image through a display screen are disclosed in Japanese Patent Application Laid-open Publication No. 2001-292276, Japanese Patent Application Laid-open Publication No. 2001-339640 and Japanese Patent Application Laid-open Publication No. 2005-327106. Proposed in these documents is an optical touch-panel for detecting a position of and contact by a finger, by use of an image received through the display screen.
Hereinafter, descriptions will be provided for an image picked up through a display screen. In a displayed image shown in FIG. 1, an image 101 is displayed in an upper portion, and key icons 102 are displayed in the lower portion thereof. A display apparatus that displays the image in FIG. 1 determines on whether or not a contact occurs between a pointing object 103 and the display screen, in the lower portion of the display screen (hereinbelow, simply referred to as a “contact determination”).
A light beam emitted from a backlight passes through a liquid crystal layer, polarizers and displays the image on the display screen. Some of the light beams reflect on an interface of the polarizers or on a protective acrylic screen disposed on a surface of the liquid crystal panel, and then enter an optical sensor. When an image is picked up in ambient light of low illuminance as can be seen in a picked-up image in FIG. 2, in some cases, brightness and darkness of the displayed image are reflected in the picked-up image. In the case where the brightness and darkness of the displayed image are reflected in the picked-up image, an error input may occur by the display apparatus wrongly recognizing that a position different from the original position of the pointing object 103 is the coordinate of contact point.